Magnetic properties of perpendicular magnetic anisotropic CoPt/Ru/CoPt thin films sputtered at room temperature

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In order to facilitate the applications at perpendicular spin-electronic devices, it is advantageous to prepare the magnetic film with a high perpendicular magnetic anisotropy (PMA) and very flat surface at room temperature. CoPt alloy film has high magnetic crystal anisotropy. In our present work, CoPt films with high PMA sputtered at room temperature are successfully obtained by introducing both Ru/Ta underlayers on SiO2/Si(100) substrates by sputtering. First, magnetic properties of Co50Pt50 thin films with Pt/Ta and Ru/Ta underlayers are compared, and thickness effect of underlayer are investigated. Co50Pt50 film on Ru/Ta exhibit comparable PMA with low coercivity(H_(C⊥)) of 69 Oe, especially for Ru(20 nm)/Ta(5 nm). On the other hand, to test CoPt/Ru(tRu)/CoPt /Ru/Ta/SiO2/Si(100) for application in the perpendicular spin valve structure, thickness of the spacer Ru layer (tRu) is modified in the range of 0.15-0.8 nm. Magnetic behavior of the above samples with tRu shows the change of ferromagnetic coupling (FC) to antiferromanetic coupling (AFC) to FC with increasing tRu, which confirms a typical RKKY interaction. Magnetic behavior of our samples in AFC state belongs to spin-flip dominated by anisotropy energy due to strong PMA in our CoPt films. However, the spin-flop contributes to mix with spin-flip when the thickness of CoPt is reduced to 3 nm due to low anisotropy energy resulted from low thickness. Besides, IrMn deposited on CoPt/Ru/CoPt/Ru/Ta to verify exchange bias. An obvious shift of M-H curve in negative field direction is found due to the coupling of the AFM and FM. Finally, CoPt/Ru/CoPt/Ru/Ta films deposited on the flexible PI tape substrates to test the applications in the wearable electronic device, and the magnetic properties with different curvatures are studied. The results of present study suggests this sputter-prepared CoPt films at RT with strong PMA could exhibit AFC state due to RKKY interaction, exchange bias resulted from the coupling between IrMn and CoPt, perpendicular GMR of 3.89 % based on spin valve structure, and AFC state for CoPt/Ru/CoPt films on flexible PI substrates. Keyword：perpendicular magnetic anisotropic, CoPt